Another good tool for this is the linear feedback shift register, and most programmers outside of crypto seem to be unaware of it too. A "complete" N-bit LFSR gives you 2^N non-repeating pseudorandom values. You start with some value (the seed), and feed it into your LFSR operation along with your chosen bitmask (the "taps"), and you get a difficult-to-predict value back out.
"Complete" LFSRs are created by carefully selecting your taps, and there's plenty of literature available for a broad range of taps for many different numbers of output bits.
Your cipher may have an LFSR buried somewhere in it, I guess they're a common component in crypto. (I know dick-all about crypto, mostly.)
Usual caveats for PRNGs apply: LFSRs are cool and magical and super fast, but the next number in the sequence can be computed by anyone else that can figure out your LFSR and seed, and since a complete LFSR will hit each value in 2^N exactly once per cycle, it doesn't even count as pseudorandom.
But, if you need a random-looking non-sequential non-repeating selection widget, an LFSR just might do the trick.
"Complete" LFSRs are created by carefully selecting your taps, and there's plenty of literature available for a broad range of taps for many different numbers of output bits.
Your cipher may have an LFSR buried somewhere in it, I guess they're a common component in crypto. (I know dick-all about crypto, mostly.)
Usual caveats for PRNGs apply: LFSRs are cool and magical and super fast, but the next number in the sequence can be computed by anyone else that can figure out your LFSR and seed, and since a complete LFSR will hit each value in 2^N exactly once per cycle, it doesn't even count as pseudorandom.
But, if you need a random-looking non-sequential non-repeating selection widget, an LFSR just might do the trick.